1. Field of the Invention
The present invention relates to an object area tracking apparatus and its control method and program.
2. Description of the Related Art
An image processing technique for automatically detecting a specific object pattern from an image is useful and can be used, for example, to specify an area of a person's face. Such an image processing technique can be used in many fields such as communication conference system, man-machine interface, security system, monitor system for tracking a person's face, image compression, and the like. In an image pickup apparatus such as digital camera, digital video camera, or the like, a specific object is detected from a photographed image and a detection result is set as a control target, thereby optimizing a focus and an exposure. For example, the Official Gazette of Japanese Patent Application Laid-Open No. 2005-318554 discloses a photographing apparatus which detects a position of a face of a person in an image to focus on the face and photographs the image under exposure which is optimum to the face. The Official Gazette of Japanese Patent Application Laid-Open No. 2009-211311also proposes image processing apparatus and method for detecting an upper half of a person's body from an image and counting the number of persons.
However, when the person's face is detected from the image, in the case where a feature of the face is not sufficiently obtained because the person is backward or the like, the face cannot be detected. In a case where the upper half of the person's body is detected from the image, even if the person is backward, the upper half can be detected. However, if the person is in a special attitude or if a portion of an area of the upper half of the person's body does not appear in the image, the upper half cannot be detected. That is, a detectable situation changes in dependence on a detecting method of the object. Therefore, in order to reduce a situation where the object cannot be detected and to improve a detection rate, a method whereby different detecting methods are used together is considered. For example, by using a result of the detection of the person's body for the object whose face could not be detected, the detection rate of the object can be improved.
There is a main object determination technique for selecting an object (main object) which is used in photographing control such as in-focusing or the like from the detected objects. In the case where a plurality of objects are detected, such a technique is used, for example, to select one main object to be subjected to adjustment of focus and exposure from the objects. The main object determination technique is required to automatically determine a target photographing object which the user intends to photograph.
By the detection of the person's body from the image, even in a state where the object is backward and the face cannot be seen, the object can be detected. However, even if the face could be detected, there is a case where the user does not want to select such a face as a main object. For example, in a scene in which a child or the like is always moving, in order to improve stability of the detection and tracking of the object, the user also wants to use detection data at the time when the person is backward or the like, as data of the main object. When such a show that a mascot is dancing is photographed, there is a case where an audience who is backward happens to be taken into a picture. In such a scene, even if the audience who is backward could be detected, the user does not want to select such an image as a main object.